Natural Kaolinite Research Articles

Comparison of Adsorption Capacity of Natural and Acid-activated Kaolinite Clay for Cesium ions from Aqueous Solution

Objectives : This study is to compare the removal efficiency of cesium ions in aqueous solutions by natural and acid-activated kaolinite clay.Methods : Natural kaolinite clay was acid-treated with H2SO4 (2M) at 80oC for 6 h under mechanical stirring. While activating natural kaolinite clay with acid, cations such as Al3+, Ca2+, Mg2+ and Fe3+ were partially eluted from the crystal lattice of natural kaolinite clay, and resulted in the increase in the surface area and the pore volume through the opening of crystal lattice. The surface area and the pore volume of acid-activated kaolinite clay were found to be roughly three times higher than natural kaolinite clay. The characteristics of natural and acid-activated kaolinite clay were observed by X-ray Fluorescence Spectroscopy, Energy Dispersive X-ray Spectroscopy, and BET Surface Area Analyzer.Results and Discussion : Generally, adsorption efficiency of Cs+ ion by acid-activated kaolinite clay showed much higher compared with natural kaolinite clay. At 50 mg L-1 of Cs+ ion concentration and the unit of dose in g L-1 , the adsorption efficiencies of Cs+ ion by natural and acid-activated kaolinite clay were 57.5% and 96.9%, respectively. The data obtained from this study were fitted to the adsorption isotherm and the kinetic models, respectively. It revealed that the Langmuir isotherm and the pseudo-second-order kinetic models described well the adsorption behavior of Cs+ ions on both natural and acid-activated kaolinite clay owing to their higher correlation coefficient R2. Based on the Langmuir isotherm coefficient Q, adsorption capacity of Cs+ ion by natural kaolinite clay and acid-activated kaolinite clay were 5.65 mg g-1 and 10.6 mg g-1, respectively.Conclusion : The results demonstrated that acid-activated kaolinite clay with acid treatment can be used as more effective adsorbent for the adsorption of Cs+ ions from aqueous solution than natural kaolinite clay.

Single step synthesis of sulfidated nanoscale iron modified kaolin clay for hexavalent chromium remediation from groundwater

Remediation of dissolved hexavalent chromium [Cr(VI)] is often achieved by iron nanoparticles [nZVI], sulfidated nZVI [SnZVI], and adsorption on clay minerals. Although different types of nZVI effectively removed Cr(VI), performance evaluation of nZVI modified with low-cost and naturally available kaolinite clay was not thoroughly studied. In the present research, kaolin was modified with nZVI (K-nZVI) and SnZVI (K-SnZVI) at two different kaolin to iron mass ratios (kaolin: Fe). Both K-nZVI and K-SnZVI were synthesized by a simple one-step process, avoiding complicated amalgamation methods of modified nZVI. Effects of ionic strength, pH, major cations, and anions in Cr(VI) remediation efficiencies were probed. Kinetics of Cr(VI) removal was quantified from sacrificial batch studies. Further experiments were performed in Cr(VI)-spiked synthetic groundwater matrix in the respective pH and initial Cr(VI) ranges of 5.5–8 and 2–100 mg L−1. With maximum Cr(VI) remediation efficiencies of 100% (K-nZVI) and 98% (K-SnZVI) in synthetic groundwater contaminated with 2–100 mg L−1 Cr(VI), both of these materials might be effectively used for groundwater treatment. The usage of kaolin—an analog of the natural kaolinite clay—with relatively decreased Fe content in the nanoparticles would reduce the treatment cost and provide insight into a sustainable solution for Cr(VI) contamination.

Investigating the Influence of Impurity Defects on the Adsorption Behavior of Hydrated Sc3+ on the Kaolinite (001) Surface Using Density Functional Theory.

In natural kaolinite lattices, Al3+ can potentially be substituted by cations such as Mg2+, Ca2+, and Fe3+, thereby influencing its adsorption characteristics towards rare earth elements like Sc3+. Density functional theory (DFT) has emerged as a crucial tool in the study of adsorption phenomena, particularly for understanding the complex interactions of rare earth elements with clay minerals. This study employed DFT to investigate the impact of these three dopant elements on the adsorption of hydrated Sc3+ on the kaolinite (001) Al-OH surface. We discerned that the optimal adsorption configuration for hydrated Sc3+ is Sc(H2O)83+, with a preference for adsorption at the deprotonated Ou sites. Among the dopants, Mg doping exhibited superior stability with a binding energy of -4.311 eV and the most negative adsorption energy of -1104.16 kJ/mol. Both Mg and Ca doping enhanced the covalency of the Al-O bond, leading to a subtle shift in the overall density of states towards higher energies, thereby augmenting the reactivity of the O atoms. In contrast, Fe doping caused a pronounced shift in the density of states towards lower energies. Compared to the undoped kaolinite, Mg and Ca doping further diminished the adsorption energy of hydrated Sc3+ and increased its coordination number, while Fe doping elevated the adsorption energy. This study offers profound insights into understanding the role of dopant elements in the adsorption of hydrated Sc3+ on kaolinite.

Zeolites Derived from Natural Kaolinite for CO2 Adsorption

This manuscript deals with the synthesis of different types of zeolites from natural kaolinite samples for CO2 adsorption. A zeolite A was prepared from kaolinite by means of an alkaline fusion process, followed by hydrothermal treatment, whereas a highly crystalline zeolite X was synthesized by optimizing the previously mentioned synthetic procedure. In detail, the SiO2/Al2O3 molar ratio in the preliminary mixture was modified with the addition of a secondary silicon source (sodium silicate) in order to obtain the one required for zeolites X. The physicochemical properties of the pristine clay and of the different zeolites were investigated by means of a multi-technique approach, including XRPD; SEM-EDX; 23Na, 27Al and 29Si MAS NMR spectroscopy; and N2 physisorption analysis at 77 K. Since the Si and Al molar ratios and reactivities are key parameters for the synthesis of zeolites, these aspects, primarily related to the use of a naturally occurring aluminosilicate as the raw material, have been investigated for their correlation with the physicochemical properties of the synthetic products. Moreover, by means of a custom-built volumetric apparatus, the CO2 adsorption capacity of the resulting zeolites at low gas pressures (<1 bar) and at 25 °C was assessed.

Impacts of kaolinite enrichment on biochar and hydrochar characterization, stability, toxicity, and maize germination and growth

In this study, biochar (BC) and hydrochar (HC) composites were synthesized with natural kaolinite clay and their properties, stability, carbon (C) sequestration potential, polycyclic aromatic hydrocarbons (PAHs) toxicity, and impacts on maize germination and growth were explored. Conocarpus waste was pretreated with 0%, 10%, and 20% kaolinite and pyrolyzed to produce BCs (BC, BCK10, and BCK20, respectively), while hydrothermalized to produce HCs (HC, HCK10, and HCK20, respectively). The synthesized materials were characterized using X-ray diffraction, scanning electron microscope analyses, Fourier transform infrared, thermogravimetric analysis, surface area, proximate analyses, and chemical analysis to investigate the distinction in physiochemical and structural characteristics. The BCs showed higher C contents (85.73–92.50%) as compared to HCs (58.81–61.11%). The BCs demonstrated a higher thermal stability, aromaticity, and C sequestration potential than HCs. Kaolinite enriched-BCs showed the highest cation exchange capacity than pristine BC (34.97% higher in BCK10 and 38.04% higher in BCK20 than pristine BC), while surface area was the highest in kaolinite composited HCs (202.8% higher in HCK10 and 190.2% higher in HCK20 than pristine HC). The recalcitrance index (R50) speculated a higher recalcitrance for BC, BCK10, and BCK20 (R50 > 0.7), minimal degradability for HCK10 and HCK20 (0.5 < R50 < 0.7), and higher degradability for biomass and HC (R50 < 0.5). Overall, increasing the kaolinite enrichment percentage significantly enhanced the thermal stability and C sequestration potential of charred materials, which may be attributed to changes in the structural arrangements. The ∑ total PAHs concentration in the synthesized materials were below the USEPA’s suggested limits, indicating their safe use as soil amendments. Germination indices reflected positive impacts of synthesized charred materials on maize germination and growth. Therefore, we propose that kaolinite-composited BCs and HCs could be considered as efficient and cost-effective soil amendments for improving plant growth.

Assessment of the Effects of Boron Nitride Nanoplatelets Reinforcement on the Physical and Mechanical Properties of the Geopolymer Prepared by Natural Kaolinite: An In Vitro Study

Introduction: We aimed to assess the effects of the addition of boron nitride nanoplatelets on the physical and mechanical properties of the geopolymer prepared by natural kaolinite. Methods: The compressive strength and diametral tensile strength tests were conducted according to BS 1881-116:1983 and ASTM E9-89a(2000) using an atomic force max instrument. The surface microhardness of the geopolymer was evaluated using a Digital Vickers microhardness tester, following the guidelines outlined in ASTM E92-82(2003). The contact angle (wettability) tests were carried out according to ASTM D7334-08(2022). Results: There were statistically significant differences among all study groups regarding compressive strength, diametral tensile strength, surface hardness, and wettability (p &lt; 0.001). Conclusion: The boron nitride nanoplatelets reinforcement has a significant impact on the compressive strength, diametral tensile strength, surface microhardness, and wettability of the geopolymer, providing valuable insights for future research and development in this field.

Box–Behnken design for the optimisation of Kabachnik–Fields reaction catalysed by natural kaolinite clay under eco-friendly conditions

Kaolin catalysed the Kabachnik–Fields reaction. Box–Behnken design optimisation. Green chemistry conditions.

Advanced Equilibrium Modeling for the Synergetic Effect of β-Cyclodextrin Integration on the Adsorption Efficiency of Methyl Parathion by β-Cyclodextrin/Exfoliated Kaolinite Nanocomposite.

Exfoliated kaolinite nanosheets (EXK) and their hybridization with β-cyclodextrin (β-CD/EXK) were evaluated as potential-enhanced adsorbents of methyl parathion (MP) in synergetic investigations to determine the effects of the different modification procedures. The adsorption behaviors were described on the basis of the energetic steric and energetic factors of the specific advanced equilibrium models (monolayer model of one energy). The functionalization process with β-CD enhanced the adsorption behaviors of MP considerably to 350.6 mg/g in comparison to EXK (291.7 mg/g) and natural kaolinite (K) (244.7 mg/g). The steric studies revealed a remarkable improvement in the quantities of the existing receptors after exfoliation (Nm = 134.4 mg/g) followed by β-CD hybridization (Nm = 162.3 mg/g) as compared to K (75.7 mg/g), which was reflected in the determined adsorption capacities of MP. Additionally, each active free site of β-CD/EXK can adsorb about 3 molecules of MP, which occur in a vertical orientation by types of multimolecular mechanisms. The energetic investigations of Gaussian energy (<8.6 kJ/mol) and adsorption energy (<40 kJ/mol) validate the physical adsorption of MP, which might involve the cooperation of dipole bonding forces, van der Waals, and hydrogen bonding. The properties and entropy values, free enthalpy, and intern energy as the investigated thermodynamic functions declared the exothermic and spontaneous behaviors of the MP adsorption.

First-principles analysis on phase transition, atomic, electronic, and mechanical properties of kaolinite under pressures

Kaolinite is the major clay mineral and dispersed widely in topsoil and subsoil in the world. The structural, electronic, and mechanical properties of kaolinite are closely related to their various applications in architecture, industry, and agriculture. In the present paper, the phase transition, atomic structural, electronic and mechanical properties of kaolinite under pressure range of 0–10 GPa were systematically investigated using the first-principles density functional theory (DFT). The lattice parameters, bonding nature, total and partial density of states, elastic constants, various modulus, and anisotropy for kaolinite were calculated. The transition pressures of kaolinite occurred at 4.93 GPa (kaolinite-I → kaolinite-II) and 8.23 GPa (kaolinite-II → kaolinite-III), respectively, which were well consistent with experimental data. In the range of 0–10 GPa, the lattice parameters, volume, and typical bond lengths of I, II, and III phases of kaolinite were decreased with increasing pressure. Meanwhile, the calculated density of states, charge density distribution, and band structures had little change with increasing pressure, implied that effects of pressure on electronic property of three phases of kaolinite were weak and corresponding structures were stable. Finally, the elastic constants results of I, II, and III phases of kaolinite implied that (001) plane anti-deformation ability was weaker than (100) and (010) planes and shear deformation resistance of (001) was stronger than these of (100) and (010) plane. The results of bulk modulus, shear modulus, and Young's modulus of the three phases of kaolinite indicated that the ability of kaolinite to resist volume deformation and shear failure was enhanced. Various mechanical quantities were evaluated and implied that the kaolinite-I and kaolinite-II was ductile, while the kaolinite-III in the brittle manner. The present theoretical calculations results are helpful to understand the physico-chemical and mechanical properties of natural kaolinite from the microscopic point of view and provided an important theoretical basis for the application of kaolinite in fields of architecture, industry, and agriculture.

Swift Removal of the Heavy Metals Cadmium and Lead from an Aqueous Solution by a CAN-Zeolite Synthesized from Natural Clay

CAN-zeolite was synthesized with a high purity from natural kaolinite via alkali fusion by hydrothermal treatment at a pressure of 1 kbar H2O. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy and nitrogen adsorption at 77 K. The results show that after AK hydrothermal treatment (under specific conditions), the SBET increases from 5.8 m2g−1 to 30.07 m2g−1 which is six times greater. The AK which was a non-porous or macroporous solid (the nitrogen adsorption/desorption of AK is of type II) became mesoporous (N2 adsorption–desorption isotherms exhibit typical hysteresis of type IV) with a pore size of 5.9 Å. XRD of AK shows the presence of quartz (Q) as impurities, and illite and kaolinite as major fractions; after hydrothermal treatment, the XRD diffractogram shows only fine pics related to CAN-zeolite (with a good crystallinity), confirming the success of the synthesized process. These results suggest that the synthesized CAN-zeolite has the potential to be tested in the removal of heavy metals from waste water as part of a remediation process. Batch reactors were used to evaluate the adsorption isotherms and kinetic studies of heavy metals, cadmium, and lead, by natural kaolinite clay (AK) and synthesized cancrinite zeolite (CAN-zeolite). The results show that the adsorption kinetics of the bivalent heavy metals cadmium and lead are extremely fast with either AK or CAN-zeolite. Equilibrium was reached within 2 min. Adsorption isotherms show that the synthesized CAN-zeolite has a higher adsorption capacity; the retention capacity of lead and cadmium was three times greater than that presented by the natural clay mineral. According to the findings, CAN-zeolite has a higher affinity for PbII (192 mg/g) compared to CdII (68 mg/g). The negative reactive surface sites interacting with these cationic heavy metals resulted in a higher amount of heavy metals adsorption than the cation exchange capacity (CEC). The adsorption information was analyzed using the Langmuir and Freundlich equations. The Langmuir model provided a good fit to the equilibrium data, indicating a monolayer adsorption mechanism.

Understanding the release, migration, and risk of heavy metals in coal gangue: An approach by combining experimental and computational investigations

The lack of understanding on the environmental fate and implications of heavy metals in coal gangue (CG) has restrained its utilization. Conventional extraction methods provide empirical measures of heavy metal speciation, lacking a detailed description of bound strength, which limits long-term risk assessment. In this study, the releasing and migrating behavior of six heavy metals (Cd, As, Pb, Ni, Cu, and Cr) were investigated through an approach by combining experimental and computational investigations. The corresponding mechanisms and risks were understood and discussed on a molecular level. The results suggested that CG is primarily a natural kaolinite α-quartz and anatase mineral. The sequence extraction results showed that heavy metals in CG are mainly distributed in stable silicate and iron manganese oxide-bound states. The toxicity characteristic leaching procedure test advised Cu, Cr, Ni, and Pb had a high toxic level and thus required long-term monitoring and controlling. A quantum chemical calculation demonstrated that the heavy metals were more likely to be embedded in silicate minerals with high binding energy than those binding on the anatase surface. The findings of this research provide a promising approach to comprehensively evaluate the stability mechanism and potential long-term risks of heavy metals in solid waste.

High-pressure Raman scattering and X-ray diffraction study of kaolinite, Al2Si2O5(OH)4

Kaolinite is formed by weathering of continental crustal rocks and is also found in marine sediments in the tropical region. Kaolinite and other layered hydrous silicate minerals are likely to play a vital role in transporting water into the Earth's interior via subducting slabs. Recent studies have experimentally documented the expansion of the interlayer region by intercalation of water molecules at high pressures i.e., pressure-induced hydration. This is counter-intuitive since the interlayer region in the layered silicates is quite compressible, so it is important to understand the underlying mechanism that causes intercalation and expansion of the interlayer region.To address this, we explore the high-pressure behavior of natural kaolinite from Keokuk, Iowa. This sample is free of anatase impurities and thus helps to examine both low-energy (0–1200 cm−1) and high-energy hydroxyl (3000–4000 cm−1) regions using Raman spectroscopy and synchrotron-based powder X-ray diffraction.Our results show that the pressure dependence of the hydroxyl modes exhibits discontinuities at ∼3 GPa and ∼ 6.5 GPa. This is related to the polytypic transformation of Kaolinite from K-1 to K-II and K-II to K-III phase. Several low-energy Raman modes' pressure dependence also exhibits similar discontinuous behavior. The synchrotron-based powder X-ray diffraction results also indicate discontinuous behavior in the pressure dependence of the unit-cell volume and lattice parameters. The analysis of the bulk and the linear compressibility reveals that kaolinite is extremely anisotropic and is likely to aid its geophysical detectability in subduction zone settings. The K-I to K-II polytypic transition is marked by the snapping of hydrogen bonds, thus at conditions relevant to the Earth's interior, water molecules intercalate in the interlayer region and stabilize the crystal structure and help form the super-hydrated kaolinite which can transport significantly more water into the Earth's interior.

Microwave-Assisted Synthesis of Zeolite A from Metakaolinite for CO2 Adsorption.

The global demand for energy and industrial growth has generated an exponential use of fossil fuels in recent years. It is well known that carbon dioxide (CO2) is mainly produced, but not only from fuels, which has a negative impact on the environment, such as the increasing emission of greenhouse gases. Thus, thinking about reducing this problem, this study analyzes microwave irradiation as an alternative to conventional heating to optimize zeolite A synthesis conditions for CO2 capture. Synthesis reaction parameters such as different temperatures (60-150 °C) and different time durations (1-6 h) were evaluated. The CO2 adsorption capacity was evaluated by CO2 adsorption-desorption isotherms at 25 °C and atmospheric pressure. The results showed that the synthesis of zeolite A by microwave irradiation was successfully obtained from natural kaolinite (via metakaolinization), reducing both temperature and time. Adsorption isotherms show that the most promising adsorbent for CO2 capture is a zeolite synthesized at 100 °C for 4 h, which reached an adsorption capacity of 2.2 mmol/g.

Synthesis of a green ALG@KLN adsorbent for high-efficient recovery of rare earth elements from aqueous solution

The increasing consumption of rare earth elements (REEs) and disposal of REE-containing wastes pose a threat to resources and environment. Hence, it is important to achieve efficient REEs recovery while use eco-friendly methods. Herein, natural kaolinite is loaded on alginate hydrogel to prepare ALG@KLN composites via a facile one-step cross-link reaction without any hazardous chemicals. The characterizations of ALG@KLN, adsorption isotherms, adsorption kinetics, and desorption were investigated by SEM-EDS, XPS, FT-IR, and Zeta-potential. The maximum adsorption capacity of Gd (Ⅲ), Y (Ⅲ), Ho (Ⅲ), and Nd (Ⅲ) reached 74.40, 84.48, 85.18, and 75.17 mg/g, respectively. The adsorption kinetics and isotherm were well fitted to pseudo-second-order model and Langmuir model, respectively. The ∼2 mm diameter ALG@KLN can be easily collected and reused. The presence of Na+, Mg2+, and Al3+ has a minor effect on the adsorption of REEs. The adsorption mechanism is mainly via the chemical chelation of oxygen-containing functional groups and electrostatic interaction on negatively charged surface of ALG@KLN. In addition, the cost of ALG@KLN is as low as ∼0.041 USD/gram. This work greatly contributes to the development of economical and eco-friendly REE adsorbents, which plays an important role in sustainable development.

Synthesis and Characterization of β-Cyclodextrin-Hybridized Exfoliated Kaolinite Single Nanosheets as Potential Carriers of Oxaliplatin with Enhanced Loading, Release, and Cytotoxic Properties.

Natural kaolinite was subjected to a successful exfoliation process into separated kaolinite nanosheets (KNs), followed by hybridization with β-cyclodextrin biopolymer (β-CD), forming an advanced bio-nanocomposite (β-CD/KNs). The synthetic products were evaluated as enhanced delivery structures for oxaliplatin chemotherapy (OXAPN). The hybridization of KNs with β-CD polymer notably enhanced the loading capacity to 355.3 mg/g (β-CD/KNs) as compared to 304.9 mg/g for KNs. The loading of OXAPN into both KNs and β-CD/KNs displayed traditional pseudo-first-order kinetics (R2 > 0.85) and a conventional Langmuir isotherm (R2 = 0.99). The synthetic β-CD/KNs validates a greater occupied effective site density (98.7 mg/g) than KNs (66.3 mg/g). Furthermore, the values of the n steric parameter (4.7 (KNs) and 3.6 (β-CD/KNs)) reveal the vertical orientation of the loaded molecules and the loading of them by multi-molecular mechanisms. These mechanisms are mainly physical processes based on the obtained Gaussian energy (<8 KJ/mol) and loading energy (<40 KJ/mol). The release profiles of both KNs and β-CD/KNs extend for about 120 h, with remarkably faster rates for β-CD/KNs. According to the release kinetic findings, the release of OXAPN displays non-Fickian transport behavior involving the cooperation of diffusion and erosion mechanisms. The KNs and β-CD/KNs as free particles showed considerable cytotoxicity and anticancer properties against HCT-116 cancer cell lines (71.4% cell viability (KNs) and 58.83% cell viability (β-CD/KNs)). Additionally, both KNs and β-CD/KNs significantly enhanced the OXAPN's cytotoxicity (2.04% cell viability (OXAPN/KNs) and 0.86% cell viability (OXAPN/β-CD/KNs).

Insight into the Morphological Properties of Nano-Kaolinite (Nanoscrolls and Nanosheets) on Its Qualification as Delivery Structure of Oxaliplatin: Loading, Release, and Kinetic Studies

Natural kaolinite underwent advanced morphological-modification processes that involved exfoliation of its layers into separated single nanosheets (KNs) and scrolled nanoparticles as nanotubes (KNTs). Synthetic nanostructures have been characterized as advanced and effective oxaliplatin-medication (OXAP) delivery systems. The morphological-transformation processes resulted in a remarkable enhancement in the loading capacity to 304.9 mg/g (KNs) and 473 mg/g (KNTs) instead of 29.6 mg/g for raw kaolinite. The loading reactions that occurred by KNs and KNTs displayed classic pseudo-first-order kinetics (R2 &gt; 0.90) and conventional Langmuir isotherms (R2 = 0.99). KNTs exhibit a higher active site density (80.8 mg/g) in comparison to KNs (66.3 mg/g) and raw kaolinite (6.5 mg/g). Furthermore, compared to KNs and raw kaolinite, each site on the surface of KNTs may hold up to six molecules of OXAP (n = 5.8), in comparison with five molecules for KNs. This was accomplished by multi-molecular processes, including physical mechanisms considering both the Gaussian energy (&lt;8 KJ/mol) and the loading energy (&lt;40 KJ/mol). The release activity of OXAP from KNs and KNTs exhibits continuous and regulated profiles up to 100 h, either by KNs or KNTs, with substantially faster characteristics for KNTs. Based on the release kinetic investigations, the release processes have non-Fickian transport-release features, indicating cooperative-diffusion and erosion-release mechanisms. The synthesized structures have a significant cytotoxicity impact on HCT-116 cancer cell lines (KNs (71.4% cell viability and 143.6 g/mL IC-50); KNTs (11.3% cell viability and 114.3 g/mL IC-50). Additionally, these carriers dramatically increase OXAP’s cytotoxicity (2.04% cell viability, 15.4 g/mL IC-50 (OXAP/KNs); 0.6% cell viability, 4.5 g/mL IC-50 (OXAP/KNTs)).

Convert waste to MOF: Nitro-MIL-53(Al) synthesized from waste acid leachate for highly efficient capture of p-nitrophenol

As inspired by the sustainable concept of “turning waste into materials”, a feasible "killing three birds with one stone" strategy was proposed to design and synthesize Al-based MOF material from Al-rich acid leachate of natural kaolinite for capture of p-nitrophenol (PNP). The acid leachate neutralized with aluminum compound, as Al sources and reaction medium, was directly reacted with nitroterephthalic acid (NTPA) to form Al-MOF (named Nitro-MIL-53(Al)), so that the harmless disposal of acidic wastewater, the recovery of valuable metal, and the synthesis of new materials were achieved simultaneously. The porous Nitro-MIL-53(Al) adsorbent has superb adsorption capacity (173.01 mg/g) and removal efficiency (95.76 %, at 400 mg/L) towards PNP, and can be regenerated and reused more than 4 times. It still maintains higher adsorption capability of 117.76–153.21 mg/g for PNP in the waters containing different amounts of co-existing ions, respectively. The comprehensive analyses on structures and adsorption behaviors revealed that PNP was adsorbed onto Nitro-MIL-53(Al) by a chemisorption process, and π-π interaction, hydrogen bonds, and electrostatic attraction synergically contribute to the adsorption of PNP. This research provides a sustainable way to achieve simultaneously harmless disposal of waste liquid and development of new adsorption materials.

Food packaging composite film based on chitosan, natural kaolinite clay, and Ficus. carica leaves extract for fresh-cut apple slices preservation

The problem of environmental plastic contamination is one of the most serious issues facing our world today. The majority of the packaging materials used to preserve food are made of plastic which is considered an environmental issue. Natural kaolinite clay (KC) and Ficus leaf extract (FLE) were combined with chitosan in this work to create a novel antioxidant and biodegradable food packaging film. Chitosan/KC/FLE film was compared to chitosan film, Chitosan/KC, and Chitosan/FLE films in terms of structural, physical, and functional aspects. The addition of FLE and/or KC significantly improved the light and moisture barrier characteristics, mechanical properties, and antioxidant capabilities of chitosan film. Moreover, KC addition had a remarkable impact on the water vapor permeability and the biodegradability of the chitosan film. Because of the synergistic action of FLE and KC, the Chitosan/KC/FLE film delivered strong barrier and antioxidant capabilities. Furthermore, Chitosan/KC/FLE film was tested as packaging material on fresh-cut apple slices and demonstrated good food preservation regarding the weight loss, browning index, and total phenolic content of the fruit. According to our findings, Chitosan/KC/FLE film might be employed as a possible food packaging material in the food industry.

A combined molecular dynamics simulation, DFT calculations, and experimental study of the adsorption of Rhodamine B dye on kaolinite and hydroxyapatite in aqueous solutions

The adsorption efficiency of Rhodamine B (RhB) onto the natural kaolinite and hydroxyapatite (HAP) was investigated. Both adsorbents were characterized using XRD, FTIR, SEM, XRF, and BET surface area analysis. The experimental adsorption tests were optimized by the Box-Behnken design (BBD) which led to conclude the maximal RhB removal obtained by kaolinite (95%) and HAP (84%) using pH=6.5, [RhB]=60 mg/L, and adsorbent mass=1.5 g/L. Molecular dynamics (MD) simulations were finally applied to investigate and predict the mechanisms involved in the adsorption of RhB molecules onto the surface of the kaolinite and HAP. This indicated that the adsorption phenomenon was spontaneous and favorable in the acidic medium with the dominance of Van der Waals interactions. The kinetics investigation showed that the adsorption is well described by the pseudo-second order kinetic (R2 =0.99). The thermodynamics and isotherms studies exhibit that the adsorption phenomenon for both adsorbents is endothermic and significantly fitted with the Freundlich model. The significant RhB adsorption efficiency suggests the potential application of the natural HAP and kaolinite for the removal of the dyes. Moreover, the theoretical study would be of interesting contribution to the advances in the proposed mechanisms of the adsorption process.

Kaolinite subgrade strength characteristics variation with RBI Grade 81

The shrinking behaviour of clay soil due to moisture variation causes damage to the foundation of structures, residential, commercial structures and embankment construction. To overcome this problem, the soil needs to be treated to improve its strength and durability of the ground. The best technique is stabilization, which enhances the engineering soil properties, upgrades the shear strength, and reduces the consistency limit. In this present study, Kaolinite clayey subgrade soil is stabilized using Road Building International Grade 81 (RBI), and its effects on the strength characteristics of the soil are studied. Compaction characteristics, Atterberg's limits, Unconfined Compression Strength tests (UCS), and Split Tensile Strength (STS) on the soil samples were performed. The same composites are studied for SEM and XRD results to confirm the morphology of the new compounds formed. Compaction factors increased optimum moisture content (OMC), and the maximum dry density (MDD) decreased with RBI Grade 81 to kaolinite. UCS values increased significantly for the clayey subgrade with the addition of RBI Grade 81. RBI Grade 81 at 8% shows an enhanced upgrade in the clay subgrade's strength compared with the natural kaolinite subgrade. Hence, RBI Grade 81 can be recommended as a potential soil stabilizing agent, particularly for clayey subgrade soil.